Metal cutting has to meet ever-increasing demands on productivity and machining speeds. Friction during machining, workpiece and cutter wear are the leading causes of reduced productivity. According to the German Tribological Society report, in industrialized countries, losses caused by friction and wear alone account for 5% of the social output value every year. Coatings can improve the friction and wear properties of tools and are essential in cutting. Surface treatment technology providers have been developing customized coating solutions to improve tool wear resistance, machining efficiency, and service life for many years.
To sum up, cutting tool surface coating technology has the following characteristics:
1. The use of coating technology can significantly improve the surface hardness of the tool without reducing the strength of the device, and the hardness that can be achieved at present is close to 100GPa;
2. With the rapid development of coating technology, the chemical stability and high-temperature oxidation resistance of the film are prominent, thus making high-speed cutting possible;
3. The lubricating film has good solid-phase lubrication performance, which can effectively improve the processing quality and is also suitable for dry cutting;
4. Coating technology, as the final process of tool manufacturing, has little effect on tool accuracy and can carry out repeated coating processes.
The benefits of coated cutting tools: can significantly improve the life of cutting tools; effectively improve the cutting efficiency; significantly improve the surface quality of the workpiece to be processed; effectively reduce the consumption of tool materials and reduce processing costs; reduce coolant consumption. Use, reduce costs and be conducive to environmental protection.
Proper surface treatment of small round tools can increase tool life, reduce cycle times and improve machined surface quality. However, choosing the right tool coating for machining needs can be confusing and laborious. Each layer has advantages and disadvantages in machining. Selecting the wrong coating can result in lower tool life than uncoated tools and sometimes even more problems than before the coating.
Common Coatings for Tools
1. Diamond, diamond-like carbon (DLC) coating
Diamond coating is one of the new tool coating materials. It uses low-pressure chemical vapor deposition technology to grow a layer of the diamond film composed of polycrystals on the cemented carbide substrate. It uses it to process non-ferrous metals such as silicon aluminum alloy and copper alloy engineering materials such as glass fiber, cemented carbide, and other materials. The tool life is 50 to 100 times that of standard carbide tools. Many diamond synthesis techniques are used for diamond coating: hot wire, microwave plasma, and DC plasma jet. By improving the coating method and the bonding of the layers, diamond-coated tools have been produced and used in industry.
In recent years, countries such as the United States, Japan, and Sweden have successively launched diamond-coated taps, reamers, milling cutters, and diamond-coated carbide drills for processing small holes on printed circuit boards and various indexable Blades, such as CD1810 of Sweden Sandvik Company and KCD25 of American Kennametal Company. Turchan Company developed a new process of laser-plasma deposition of diamond in the United States. Using this method to deposit diamond, because the plasma field surrounds the entire tool, the coating on the device is uniform, and the deposition speed is 1000 times faster than that of the conventional CVD method. The diamond coating formed by this method has a natural metallurgical bond with the substrate, and the layer has high strength, which can prevent the coating from falling off, cracks and cracks, and other defects.
Diamond-like coatings have distinct advantages in machining certain materials (Al, Ti, and their composites). The microstructure of diamond-like carbon coatings deposited by low-pressure vapor deposition is still quite different from that of natural diamond. In the 1990s, low-pressure vapor deposition of DLC in the presence of activated hydrogen was often used, and the coating contained a large amount of hydrogen. Excessive hydrogen content will reduce the bonding force and hardness of the layer and increase the internal stress. The hydrogen in the DLC is slowly released at higher temperatures, causing the coating to work erratically. The hardness of DLC without hydrogen is higher than that of DLC with hydrogen, and it has the advantages of uniform structure, large-area deposition, low cost, and smooth surface. It has become a hot spot in DLC coating research in recent years. Tihao Machinery is the company’s main product with rotary top, lead screw, machine tool spindle, shaft processing, high-precision tool holder, tool holder, elastic chuck, non-standard parts processing, machine tool adapter’s main products. American scientist AAVoevodin proposed to deposit superhard. The DLC coating structure is designed as a Ti-TiC-DLC gradient transformation coating, which gradually increases the hardness from the softer steel substrate to the superhard DLC coating on the surface. This type of composite coating maintains high hardness and low coefficient of friction, reduces brittleness, and improves bearing capacity, bonding force, and wear resistance. Sumitomo Corporation of Japan has launched the DL1000 coating coated with diamond DLC on cemented carbide inserts, which is used to cut aluminum alloys and non-ferrous metals, resist sticking, and effectively reduce the roughness of the machined surface.
After years of research, it has been shown that due to the high internal stress, poor thermal stability, and the catalytic effect between the DLC coating and the catalytic impact between the ferrous metals. The SP3 structure is transformed into SP2, etc., which determines that it can only be used in the processing of non-ferrous metals at present. For its further application in machining. However, recent studies have shown that the hardness of diamond-like coatings (also known as graphite-like coatings) based on SP2 structure can also reach 20-40GPa. Still, there is no problem of catalytic effect with ferrous metals, and its friction coefficient is very high. It has low temperature and good moisture resistance. It can be used with coolant or dry cutting during cutting. Its life is doubled compared with uncoated knives. Great interest. In time, this new type of diamond-like coating will be widely used in the cutting field.
2. Cubic boron nitride (CBN) coating
CBN is another super hard material after synthetic diamond. In addition to having many excellent physical and chemical properties similar to diamond (such as ultra-high hardness, second only to diamond, high wear resistance, low friction coefficient, low In addition to thermal expansion coefficient, etc.), it also has some properties better than diamond. Taihao Machinery is the company’s main product with rotary top, lead screw, machine tool spindle, shaft processing, high-precision tool holder, tool holder, elastic chuck, non-standard parts processing, and machine tool adaptor. CBN is chemically inert to iron, steel, and oxidizing environments and forms a thin layer of boron oxide when oxidized. This oxide provides chemical stability to the coating, which is also heat resistant when machining hard iron and gray cast iron. Extremely excellent, it can also cut heat-resistant steel, quenched steel, titanium alloy, etc., at a relatively high cutting temperature. It can also cut high-hardness chilled rolls, carburizing and quenching materials, and silicon-aluminum alloys with severe tool wear—processing material.
Since the successful preparation of pure CBN coating by Inagawa et al. in 1987, the research upsurge of CBN hard coating has been set off in the world. The methods of low-pressure gas-phase synthesis of CBN coatings mainly include CVD and PVD methods. CVD includes chemical transport PCVD, hot wire assisted heating PCVD, ECR-CVD, etc.; PVD includes reactive ion beam plating, active, reactive evaporation, and laser evaporation ion beam assisted deposition. The research results show that progress has been made in synthesizing the CBN phase, good adhesion to cemented carbide substrate and suitable hardness, and the maximum cubic boron nitride deposited on cemented carbide is only 0.2～0. 5μm, if you want to achieve commercialization, you must use reliable technology to deposit a high-purity and economical CBN coating, and its thickness should be 3-5μm. Its effect is confirmed in actual metal cutting.
3. CNx coating
In the 1980s, American scientists Liu and Cohen designed a new compound, β-C3N4, similar to β-Si3N4. It uses the theory of solid-state physics and quantum chemistry. It was calculated that its hardness might reach that of a diamond, which attracted the attention of scientists from all over the world. The synthesis of carbon nitride has become a hot topic in material science in the world. The carbon nitride coating obtained by FFujimoto of Okayama University in Japan by electron beam evaporation and ion beam assisted deposition method reaches 63.7Gpa. The hardness of carbon nitride synthesized by Wuhan University comes 50GPa, respectively, and it is deposited on the high-speed steel twist drill to obtain excellent drilling performance. The main methods of synthesizing carbon nitride are accurate flow and radiofrequency reactive sputtering, laser evaporation and ion beam assisted deposition ECR-CVD, double ion beam deposition, etc.
The global tool market exceeds 37 billion US dollars
The size of the worldwide tool market is growing steadily. According to QY Research data, the global consumption of cutting tools will reach US$37 billion in 2020, with a compound growth rate of 2.82% from 2016 to 2020.
The national cemented carbide cutting tool market scale exceeds 20 billion yuan. According to the fourth user survey of metal processing, cemented carbide tools accounted for 53% of the domestic tool market demand in 2019. Based on this, it is estimated that the domestic tool market will be about 20.8 billion yuan in 2019 and about 23.6 billion yuan in 2020; according to China’s machine tool industry According to the association, blades account for about 50% of the sales of cemented carbide cutting tools of member companies. Based on this, it is estimated that the domestic cemented carbide blade market size is about 10 billion yuan. According to the China Tungsten Industry Association, carbide inserts can be divided into CNC inserts, welded inserts, standard indexable inserts, and other cutting inserts. CNC inserts are the category with the highest added value of carbide inserts.
Global tool industry players are roughly divided into three echelons
At present, the competition pattern of the international cutting tool industry is roughly divided into three echelons.
The first echelon is European and American tool companies. They were leading the high-end customized tool market. European and American tool companies have a long history and strong technical force; they mainly provide customers with overall cutting solutions. The products are unique and customized with good stability, but they are expensive and have an extended delivery time. European and American companies have always occupied a dominant position in high-end customized tools, and the market presents an oligopolistic competition pattern.
The second echelon: Japanese and Korean tool companies. With high recognition of non-customized tools. The products of Japanese and Korean tool companies have high versatility, good stability, and high-cost performance. They have won the favor of many manufacturers in non-customized tools. The products of Japanese and Korean tool companies occupy a relatively high share in the consumption of imported devices in my country. They are mainly sold in domestic wholesale through distributors, and the product prices are generally higher than those of household tools.
The third echelon: Chinese tool companies are gradually catching up with Japan and South Korea in the non-customized market. There are many domestic tool companies, and the strength gap is significant, and they have won more middle and low-end market shares through price and service advantages. Domestic tool companies continue to improve their technical level, promote the localization of tools and the development of high-end domestic manufacturing, and are expected to take the lead in fostering domestic substitution in the non-customized tool market.